Trying not to swear about how much total crap this Photon UI thing is is truly daunting. 
Everything is too big, and way too much useless empty space in and around pretty much every window.
What happened to the side scroll bar clicking to where the mouse clicks?? Now it is in clickable increments. There are lots of situations in EVE with large amounts of items in a window. A prime example is the Overview and all the planets, moons, gates, stations, etc. that it can show. Before, you could click on the bottom of the side scroll bar, and it would drop the scroll down all the way. Now, clicking on the side scroll bar only scrolls a portion of it. Sometimes several clicks to get all the way to the bottom. And then when there are hundreds of items in a container! 
This becomes very apparent with Stargates that are on opposite side of a system. Before, you could one-click at the bottom of the scroll bar, and it would scroll all the way down to where opposite-side-of-the-system Stargate would show in the list.
There are lots of other situations where it is very handy to one-click to the bottom of the Overview and other scroll bars when there are numerous items displayed.
The scrolling wheel scrolling is too much. It seems like it is about every ~3 item. Possibly due to how f—ing big everything now is! Before, you could wheel scroll more or less one item at a time. 1 item per wheel scroll is better.
The windows sizing edges are more responsive than the scroll slider, and I’m ending up clicking on that more than anything. Resizing the window is one of the least things I care about!
Again, everything is too big: windows too big, buttons too big, scrolling to big, on and on. I do NOT want to play EVE with a goth variation of Candy Crush Saga as the UI overlay.
If this new Photon UI is the best new content the developers can come up with, the problem is with the developers’, not with the UI.
Star Wars: Galaxies. Many may not remember this game, because it was almost 20 years ago. They did a big revamp of that game, calling it the New Gaming Enhancement (NGE). Enhancement - kinda like the Photon UI “enhancement”? 
They swore up and down that “John Smedley, president of Sony Online Entertainment, defended the decision claiming it necessary to revamp the game in order to reverse the deterioration they were seeing in the subscriber base”. Then, later, “John Smedley admitted to “stupid decisions” regarding Star Wars Galaxies combat upgrade and new gaming enhancement policies”.
Seriously. No. We don’t want EVE NGE in the form of Photon UI “enhancements”.